This invention relates to apparatus for stacking flexible sheets, for example, sheets of paper, which have been fed seriatim along a flow-line. More specifically, the apparatus is of the type in which the leading edges of the sheets are fed up to a support surface which forms an essential part of a stacking apparatus. In operation, a first sheet is fed by a suitable feeding means along the flow-line to the support surface and the following sheets are added progressively in a direction substantially parallel to the surface of said first sheet thereby to form a stack. To control the build-up of the stack, a yieldable pressure pad member, capable of movement in a direction parallel to said support surface, is provided to engage the exposed face of said first sheet.
To facilitate the delivery of a sheet in a direction across the surface of a stack, various devices are known in the art, for example, a driven roller may be provided in frictional contact with the front face of the stack to define a convergent opening for the receipt of a further sheet. Alternatively, a tined or pocketed wheel may be provided to receive the leading edges of sheets and to convey the sheets to the support surface. In the latter instance a part of the wheel is arranged to pass through a suitable aperture formed in the support surface thereby to strip the sheets from between the tines as the wheel revolves.
Special problems are encountered when it is desired to stack sheets at a very high speed in a reliable manner, for example at a frequency of the order of twenty sheets per second. Further problems are encountered when it is desired to stack sheets that are not in perfect condition, for example the apparatus may be required to stack used banknotes at the output stage of a banknote condition-verifying machine. Such banknotes may be torn or folded and, furthermore, the structure of the paper may have weakened or degraded through use. In these circumstances a specific problem may be created after the delivery of a banknote having a damaged or folded end in so far that the said end may obstruct the passage of a following banknote and prevent the same from contacting the support surface. In the case of flat but torn or worn banknotes the weakened ends thereof may be influenced by air turbulence and their trajectories may be varied and indeterminable with the result that an obstruction is created.